In conventional cellular communication systems, radio coverage is provided for a given geographic area via multiple base stations distributed throughout the geographic area involved. In this way, each base station can serve traffic in a smaller geographic area. Consequently, multiple base stations in a wireless communication network can simultaneously serve users in different geographic areas, which increases the overall capacity of the wireless network involved.
In order to increase the capacity of certain wireless systems further, such as cellular systems, each base station may be configured to support radio coverage in multiple sectors. For example, a base station in a conventional cellular system may be configured to provide radio coverage in one sector, three sectors or six sectors. A pictorial diagram 100 depicting examples of conventional sectorized radio coverage patterns for an omni-sector base station 102, a 3-sector base station 104, and a 6-sector base station 106 are shown in FIG. 1. In those systems with multiple sectors per base station, each sector can handle part of the traffic in an additional smaller geographic area, which increases the overall capacity of the wireless network involved.
In currently deployed cellular systems, each base station typically supports 3-sector radio coverage with two receive antennas per sector. An example of such 3-sector coverage is shown in FIG. 2. The main rationale for having two receive antennas per sector is to provide 2-way receive diversity for uplink transmissions from mobile stations located in each sector's coverage area. In general, a mobile station is capable of producing only a relatively small amount of transmit power relative to that of a base station. For example, a typical base station's transmit power can be 20 dB higher than that of a mobile station. Therefore, a link-budget issue between the uplink and downlink has to be resolved, because the range of the uplink is much smaller than that of the downlink. This link budget limitation of the uplink is partly compensated for by providing two receive antennas per sector on the uplink. The two receive antennas can provide 3.0 dB receive beam-forming gain in addition to a significant amount of receive diversity gain on the uplink. This two-antenna approach is currently used to improve the uplink coverage of existing cellular systems.
It is often desirable to include more than three-sector coverage on the downlink of a cellular system, in order to allow for resource usage that can potentially improve the system's capacity. However, for example, if the number of sectors per base station is increased to six, but the total number of antennas per base station is kept at six, then only one receive antenna per sector is available. An example of such 6-sector coverage is shown in FIG. 3. Notably, this one antenna per sector approach can seriously impact the uplink coverage due to the reasons mentioned above. An alternative approach is to increase the total number of transmit antennas per base station to 12. This 12 antenna approach could be supported by a base station with 6-sector deployment and two antennas per sector. However, the primary disadvantage of such an approach is the increased complexity and cost of the base station involved.
If information is broadcast by a cellular system, the same content is transmitted simultaneously from all of the cells (or a subset of the cells) in the system involved. If the information is broadcast from a subset of the cells, the cells that are transmitting the same content are defined to belong to a single broadcast zone. An example of such broadcast coverage is shown in FIG. 4. For example, as depicted in FIG. 4, all of the 19 cells shown belong to a single broadcast zone, and each of the cells is transmitting the same information content. Therefore, it is possible for a receiver listening to the broadcast content to receive signals from all of the cells in the broadcast zone. If all of the cells in the broadcast zone are synchronized and Orthogonal Frequency Division Multiplex (OFDM) modulation is used for the transmissions, a Single Frequency Network (SFN) operation can be realized. In an SFN-based broadcast system, the signal from all of the cells in a broadcast zone can be collected at the receiver without interference, except for background noise and interference from cells not belonging to that broadcast zone. Therefore, using an SFN-based broadcast approach, the signal-to-interference-plus-noise ratio (SINR) of the received broadcast signal can be improved. As such, this approach allows for better recovery of the broadcast information. However, a disadvantage of using the above-described conventional broadcast approaches is that the number of sectors used has to be the same for both the uplink and the downlink.